Stabilising photographic silver halide emulsions with organic mercury compounds



United States Patent No Drawing. Filed Mar. 10, 1964, Ser. No. 350,673 Claims priority, applicgtion Germany, Apr. 13, 1963,

6' Claims. Ci. 96-109) ABSTRACT OF THE DISCLUSURE Light-sensitive silver halide emulsions stabilized against changing during storage by incorporation of a small amount, generally 2 to 20 milligrams per mol of silver nitrate used to make the emulsion, of a compound R -Hg--X where X is --SR or OR R can be any of certain aryl groups, R can be any of certain 5- or 6-membered heterocyclic rings, and X can also be similar heterocyclic rings bonded to the mercury through a nitrogen atom of the hetcrocycle.

The invention relates to a process for stabilizing photographic silver halide emulsions with the aid of organic mercury compounds, and a light-sensitive photographic material containing such mercury compounds.

Photographic silver halide emulsions tend to become developable spontaneously on prolonged storage even without the action of light. That is on development a varying quantity of silver salt, depending on the length and conditions of storage, is reduced to silver in areas that have not been exposed to light. This phenomenon is knownas chemical fogging. The intensity of fogging of an emulsion depends in addition on the type of emulsion and the conditions of development. With constant conditions of development, the fogging as well as the alteration in sensitivity and gradation increase with the storage time, storage temperature and relative moisture during storage. It is common practice to add stabilizing compounds to the photographic emulsion to prevent the formation of fog. Many compounds are described as additives for the prevention of fog formation, e.g., heterocyclic mercapto and imino compounds and also mercury compounds.

Many of these stabilizers are only of limited utility since they deleteriously affect other required properties of the light-sensitive emulsion. Mercury compounds particularly have a propensity to desensitization and to alteration of the gradation (H and D-curve) of the emulsion. It is one of the objects of the present invention to provide photographic emulsions which are stabilized by compounds which do not impair the sensitivity and the gradation of the silver halide emulsions.

This object has been achieved by employing organic mercury compounds of the following formula:

where R may be aryl, such as phenyl or naphthyl, which groups may be substituted, for example, by short-chained alkyl or alkoxy groups, having up to 5 carbon atoms, hydroxyl groups, halogen such as chlorine, carboxyl or sulfo groups and other photographically inert radicals, X represents a nitrogen atom as a ring member of a 5- or 6-membcred heterocyclic ring such as diazoles, 'oxazolines, triazoles, benztriazoles, imidazoles, thiodiazolines, oxodi- 'azolines, thiodiazolines, tetrazoles, tetraazaindenes, benzthiazolines, benzoxazolines or benzimidazoles. X furthermore represents the grouping SR OR where R may be a .5- or 6-membered heterocyclic ring such as diazoles, oxazoles, triazoles, benztriazoles, imidazoles, thiodiazoles, oxodiazoles, thiodiazolidines, tetrazoles, tetraazaindenes, benzthiazoles, benzoxazoles, naphthoxazoles or benzimidazoles, and these radicals may themselves be substituted, for example, by alkyl or alkoxy groups, preferably those having up to 5 carbon atoms, aryl, preferably phenyl or naphthyl, hydroxyl, mercapto, amino, or halogen, preferably chlorine or bromine and carboXyl or sulfo groups.

The following are examplesof suitable compounds:

M.P. 237 C.

I on N \N M.P. 360 C.

M.P. 208 C.

M.P. 167 C.

I CH-CH=CH1 M.P. 128 C.

(6) N C H:- a

M.P. 153 C.

M.P. 200 C. (with decomposition) NN I! ll M.P. 210215 C, (with decomposition) M.P. 360 C.

M.P. 201 C.

I g N M.P. 230 C.

M.P. 170 C.

M.P. 226 C.

O I aumQ M.P. 210 C.

M.P. 300 c.

(20) NN I] ll OHS-C S- M.P. 277 c. (21 -rr M.P. 300 c.

i i if? HgS-C c-s-(cHm-s-o o-s-H s s M.P. 171 c.

M.P. 300 c.

24 Hots T M.P. 300 c.

) Hots N \0J'S Hg M.P. 300 c.

M.P. 231 C.

On account of tautomerism, the above compounds which have an S-Hg bond might exist in the form of compounds wherein the Hg is attached to an N-atom of a heterocyclic group and wherein the S- is present as an SH group.

The compounds may be prepared from phenyl mercury acetate and the corresponding mercapto or hydroxy compounds, as described below for Compounds 1 and 3.

Preparation of Compound 1 purified by wasllingwith water and alcohol. Yield 34 g.

Compared with known stabilizers, the compounds of the present invention have the advantage of preserving clarity in the emulsion at suitable, comparatively very low, concentrations Without impairing the sensitivity and gradawith other stabilizers that are already known. Furthermore, they may be used in emulsions which contain color couplers or developers.

As binding agents for the silver halide emulsion or the light-sensitive silver halide layer can be used hydrophilic tion ofthe emulsionthus treated, as is the case for eX- film-forming agents, such as polyvinyl alcohol, carboxyample when using many other mercury compounds promethyl cellulose, alginic acid or derivatives thereof, such posed for similar purposes. The photographic properties as salts, esters or amides, starch or preferably gelatin or of silver halide emulsions and particularly the Clarity, mixtures thereof. sensitivity and gradation (characteristic curve or H and D-curve) are very well stabilized in accordance with the EXAMPLE 1 Present PP 1 To a washed cinepositive emulsion which contains 0.25

Many Stablhzers that are parilcular y f agamst mol silver halide per liter are added, in addition to the formation of fog cause a loss in the sensitivity of the usual additives Such as com ound of nobl metal 6 fresh emulsion to a degree which seriously aifects the use- 1 p S fulness of the emulsion. Other stabilizers cause a change 9; Compound 3 (dlsso Y dlmethy formamlde.) in sensitivity on storage, which change varies in extent afier'npemng pelformefi until but is always undesirable. Usually this is accompanied by f Sensltlvlty 1s reachfid- The (1111119110113 h th fl tt i of the gradation In contrast to this, the addition of the usual hardening and cross-llnklng agents, cury compounds of the present invention have an excelis then cast onto a support and tested. Fresh samples and lent stabilizing effect both on the clarity and on the gradasampl Stored for 3 days in a heating cupboard at tion and sensitivity so that these properties remain unwere developed in a p-methylaminophenol-hydroquinone changed over prolonged periods of time. developer. The results are as follows:

- Fresh emulsion Storage at 60 Compound Fogging 7 Relative Fogging Relative sensitivity sensitivity Control test o. 04 2. 5 10 0. 10 2. l 13 Compound 3. 0. 03 2. 6 10 0. O4 2. 6 10 Control test 0. 04 2. 5 11 0. 0s 2. 7 14 Compound 3. 0. 04 2. 5 10 0. 04 2. 5 10 In addition, these compounds reduce the yellow fogging EXAMPLE 2 which readily occurs in emulsions that have been fully ripened and have a steep gradation, especially upon development with developers adapted for a steep gradation and having relatively large quantities of potassium bromide.

As silver halides there may be used chlorides, bromides or mixtures thereof, if desired with a small proportion, up

A phototechnical emulsion containing approximately 0.4 mol silver halide per liter (iodo silver bromide emulsion) is treated in a similar manner to that described above during after-ripening with 10 mg. of Compound 3.

The following figures were obtained on testing a film produced with this emulsion.

Fresh emulsion Storage at Compound Fogglng 7 Relative Fogging 7 Relative sensitivity sensitivity Control test 0. 05 3.0 18 0.31 2.1 26 yellow fog. Compound 3.... 0. 04 3. 0 18 O. 06 3. 0 21 without yellow fog. Control test 0. 04 3.0 18 0.32 1.8 27 yellow tog. Compound 3..-- 0.05 3.4 19 0.05 3.0 22 without yellow log.

to about 10 mol percent, of silver iodide. The optimum EXAMPLE 3 quantity of stabilizer to be used can easily be determined for each emulsion and each stabilizer. Generally 2 to 20 mg. stabilizer per mol. AgNO are added to the emulsion. The exact amount depends on the emulsion and stabilizer. The stabilizer may be added at any stage in the production of the emulsion, preferably during the after-ripening or as additive to the casting composition.

The photographic emulsions may or may not be optically sensitized. Additional chemical ripening compounds, e.g., sulphur compounds or salts of noble metals, may be added. In addition, the emulsions may contain alkylene oxide polymerization products aschemical sta- 10 mg. per liter of Compound 5 dissolved in dimethylformamide are added to a rinsed silver bromide emulsion which is to be used for producing photographic papers and which contains 0.16 mol silver halide per liter.

Comparing this emulsion with an emulsion not containing additive, it is found after 12 months storage that the fogging after development in a p-methylaminophenol-hydroquinone developer at 30 C. for 6 minutes is only 0.03 as compared with 0.06 of the sample not containing additive. Furthermore, the sample shows no alteration in the gradation and sensitivity whereas in the sample without additive the sensitivity has increased by one step and bilizers. Also, the new stabilizers may be used together th bl k h di p d,

EXAMPLE 4 To a silver-bromide-iodide emulsion containing approximately 0.25 mol silver halide per liter there are added, in a manner similar to Example 1, 6 mg. of Compound 9 (dissolved in dimethylformamide) in addition to other additives. The following figures were obtained on testing the keeping qualities of a film produced with this We claim:

1. Photographic material comprising at least one supported light-sensitive silver halide emulsion layer containing a compound of the following formula:

wherein R represents a radical of the group consisting of a phenyl or a naphthyl, X represents --OR or -SR The following results are obtained as described in Example 4 except that 6.3 mg. of Compound 17, dissolved in dimethylformamide, are used instead of Compound 9:

and R stands for a 5- or 6-membered heterocyclic ring Fresh emulsion Storage at 60 Develop- Compound ment time Fog- '1 Relative Fog- 7 Relative ging sensitivity ging sensitivity 6 0. 05 2. 2 22 0. 08, 2. O 25 mm test 10; 0. 0s 2. s 0.1g 2. 2 21 6 0. 2. 2 0. 0 2. 2 22 Cmpmmd l 0.06 2. 4 22 0.06 2. 3 22 EXAMPLE 6 Comparison tests were made with the emulsion described in Example 4, whereby emulsions containing Compound 3 of the present invention were compared with emulsions containing 7-hydroxy-1,2,3,4,6-pentaazaindol,

containing at least two hetero atoms at least one of which is nitrogen, said compound being present in an amount that stabilizes the emulsion against storage changes.

2. Photographic material according to claim 1, wherein R is a radical of the group consisting of diazolyl, oxazolyl, triazolyl, benztriazolyl, imidazolyl, thiodiazolyl, oxodiazolyl, thiodiazolidinyl, tetrazolyl, tetraazaindenyl, benzthiazolyl, benzoxazolyl, naphthoxazolyl and benzimiwhich is one of the best known stabilizers. dazolyl.

Fresh emulsion Storage at 60 MgJkg. Fog- Relative Fog- Relative Compound emulsion ging y sensitivity ging 'y sensitivity Control test 0. 04 2. 0 10 0. 1. 80 12 Compound 3 6 0. 04 2.0 8. 5 0. 04 1. 90 8. 5 7-hydroxy-1,2,3,4,6-pentaazaindol 40 0. 04 1. 95 9. 2 0. 10 1. 90 11. 3 D0 0.06 1.95 8.8 0. 11 1.85 11.3

Control test 0. 04 1. 7 10 0. 10 1. 12

9 10 3. Photographic material according to claim 1, in 5. Photographic material according to claim 1, in which the compound has the formula: which the compound has the formula:

R 5 l C CH Hg-S-G N S OH J 6. Photographic material according to claim 1, in

which the compound has the formula:

which the compound has the formula:

No reference cited.

20 NORMAN G. TORCHIN, Primary Examiner.

J. RAUBITSCHEK, Assistant Examiner.

4. Photographic material according to claim 1, in 

1. PHTOGRAPHIC MATERIAL COMPRISING AT LEAST ONE SUPPORTED LIGHT-SENSITIVE SILVER HALIDE EMULSION LAYER CONTAINING A COMPOUND OF THE FOLLOWING FORMULA: 